1. Field of the Invention
The present invention relates to a micromechanical acceleration sensor for detecting accelerations in multiple axes, which acceleration sensors may be used as inertial sensors in safety systems, in particular for motor vehicles.
2. Description of Related Art
Micromechanical acceleration sensors are often designed as mass-spring systems for capacitive evaluation of the deflections of a seismic mass caused by mechanical forces or torques that are present. To this end, pairs of electrodes are provided which include electrodes that are either fixedly connected to a substrate or connected to a seismic mass, and which generally form plate capacitors whose capacitance is a function of the deflection of the seismic mass. For sensor elements which measure accelerations parallel to the plane of the sensor element substrate, the seismic mass is usually suspended in the same plane in which the center of gravity of the seismic mass is situated, so that when an acceleration occurs in this plane the seismic mass is also deflected in this plane.
It is known that the influence of stress effects via the substrate on the measured signal decreases when the suspension of the seismic mass or the suspensions of multiple seismic masses, and optionally also the electrodes fixedly connected to the substrate, are close together. For conventional sensor elements which convert accelerations acting parallel to the plane of the substrate or wafer into deflections of seismic masses in the same plane, such a central suspension of movable structures and fixed detection electrodes, which is desirable for reducing the sensitivity of the sensor to stress, results in a topology-dependent manner in a reduction of the detection capacitances for sensors having such a design in current processing methods.
For sensors designed to detect accelerations in multiple axes, it is known to provide a separate mass-spring system for each axis, which results in a corresponding increase in the space requirements for such sensors. This adversely affects the chip surface area requirements and therefore the manufacturing costs, and because of the unavoidable increase in component size sometimes represents a competitive disadvantage.
It is also known to provide multiaxial acceleration sensors with a seismic mass which is used to measure accelerations in multiple directions in combination with a relatively centrally situated suspension. These systems are based on the suspension of the seismic mass by use of multiple radially extending connecting bars which allow a suspended bearing of the seismic mass. Thus far, however, it has been possible to manufacture these types of systems only in complex volume micromechanical processes, making such systems correspondingly costly.